This invention is concerned with the comolding of resin-bonded nonoven batts with an uncured foam or a foamable composition and more particularly with the comolding of batts comprising inflated pneumacel fiber with foamed latex or polyurethane foam.
It is known from U.S. Pat. Nos. 3,375,211; 3,375,212 and 3,503,907 among others, to manufacture pneumacel fibers by extrusion of a solution of a polymer at a temperature above the boiling point of the major solvent component to produce a filament in which substantially all of its polymer content is in the thin walls of extremely small foam cells, to incorporate into the cells a gas which does not readily permeate the cell walls, and to allow air to diffuse osmatically into the cells to inflate them to a pressure substantially above atmospheric. Such fibers, which have densities of 0.01 g./cc. or less, may be formed into compressed, resin-bonded, nonwoven batts by processes, as taught in U.S. Pat. Nos. 3,485,711; 3,521,328 and 3,535,181 which involve deposition of the fibers as a loose, uniform batt on a continuous belt, impregnation with a thermoplastic binder in the form of a latex, drying, heating to melt the binder, compressing and cooling before release from compression to "set" the batt in its compressed form. It is also taught in U.S. Pat. No. 3,535,181 that the compressed batt can be expanded by heating to melt the binder and cooling to rebond the batt in a more open form. If done in a confined space no more than about 2-3.times. the height of the batt thickness, the resulting batt surfaces follow the contours of the confinement. Such expanded batts are softer than the compressed batts; the gradually increasing firmness with increasing load makes them more comfortable, and hence superior for seating and certain other uses.
It is also known to manufacture cushioning foams from a variety of elastomeric materials including rubbers, both natural and synthetic, and the polyurethanes. Such foams are characterized by good resistance to cushioning of small-to-moderate loads and "bottoming" under somewhat larger loads. By bottoming is meant an abrupt end of the ability to compress further with increasing load; this characteristic significantly limits utility and must be compensated in some uses by combination with other materials.
U.S. Pat. No. 3,535,181 discloses that a foamable composition or an incompletely cured froth of an elastomeric polymer can be doctored onto either one or both faces of a compressed batt of pneumacel fibers and further it is recognized that expansion of the consolidated pneumacel batt occurs under the influence of the sensible heat applied to dry a latex foam or that developed in the chemical reaction leading to a polyurethane foam. Self-bonding of that composite is partly due to penetration of the expanded pneumacel by the foam; this contribution is small, however, since the viscosity of the foam precursor greatly increases, restricting its ability to penetrate before the pneumacel batt has opened significantly. The above-noted expansion without rigid confinement of the pneumacel batt leads to uneven pneumacel and foam surfaces; the foam must be skived to flatten, creating waste material. This unevenness is an obstacle to the economical production of a composite cushion with adequate uniformity and durability.